Our studies of various virologic and immunopathologic processes that occur when viruses and parasites replicate in the ocular microenvironment comprise five areas: (1) virus induced retinal degenerative processes; (2) the possible roles of viruses in human diseases; (3) molecular diagnosis and pathogenesis of cytomegalovirus (CMV) infections in man; (4) Varicella - zoster virus (VZV) infections of the retina and (5) Toxoplasma gondii infections of the retina. We have established that murine coronavirus can induce ocular disease and may be used as a model system for studying retinal degenerative diseases. This model has many unique features. The virus is capable of inducing an acute infection in the presence of mild retinal vascular inflammation. Initial retinal damage is followed by clearance of infectious virus and progressive retinal degeneration. This is the first retinal model to demonstrate a virus induced degeneration, viral persistence, a genetic predisposition to virus induced tissue damage and a virus triggered autoimmune response. During the past year we have evaluated viral and host factors in this disease. First, we found that immune reactivity and T cells are critical factors in limiting the pathologic consequences to the retina. Second, we found the sequential development and cellular localization of viral RNA, viral protein, MHC class I, MHC class II and ICAM-1 molecules within resident ocular antigen presenting cells (RPE and ciliary body epithelium). Third, we demonstrated that apoptosis occurs in the virus infected mouse retinas. This apoptosis appears to be an indirect result of coronavirus infections and reflects a host mechansism of virus elimination within the retina. These studies support the concept that host immune factors participate in limiting the acute virus infections within the retina and may also contribute to retinal immunopathogenesis. Human CMV is a herpesvirus that is a major cause of blindness in children born with congenital infections and in immunocompromised individuals. It is difficult to study CMV latency in man. Therefore cell culture models of CMV replication and latency may provide insight into a rationale for alternative treatment modalities. We identified that CMV replicates in human RPE cells. However, there are a number of distinct differences in virus replication in RPE cells in comparison to human fibroblasts. Virus replication in RPE cells is atypically slow. Since the delayed virus replication in HRPE may be related to cellular and/or virus factors which alter virus gene expression, HCMV IE and L mRNA expression was evaluated by RT-PCR assays. HCMV IE-72 and IE-86 and L genes were expressed sequentially in HRPE cells, however, the detection of the IE mRNA was not detected until four days after primary virus infection. These factors may be critical variables in viral persistence and viral activation within the retina. In a separate series of studies we have used this in vitro model system to evaluate CMV antisense oligonucleotide (ISIS 2922) for toxicity and efficacy in human RPE cells. These studies demonstrate that the oligonucleotide, which did not alter cell growth or morphology, did dramatically inhibit CMV replication in HRPE cells. These studies demonstrate the utility of this CMV model system to evaluate virus replication and efficacy of antiviral therapy. Human VZV infections of the eye can result in keratitis, uveitis, acute retinal necrosis or progressive outer retinal necrosis in AIDS patients. However, a small animal model that replicates these diseases does not yet exist. We have shown that intravitreal inoculation of guinea pigs with VZV results in a chronic uveitis consisting of a mononuclear cell infiltrate in the posterior segment of the eye. Using a recombinant VZV that expresses beta-galactosidase, we detected expression of the enzyme in the eye for up to four months after intraocular inoculation. This VZV mutant expressing beta-galactosidase provides a tool to explore new drugs and vaccines as well as the pathogenesis of chronic viral induced uveitis.